Abstract Alcohol ignition interlocks that prevent drivers who have been drinking from starting their vehicles have become one of the most widely used and rapidly growing methods for controlling the risk that individuals convicted of driving while impaired (DWI) present to the driving public. Research has shown that offenders can learn to drive with an interlock and avoid lockouts without substantially reducing the quantity of alcohol they consume or curtailing their driving. What is not known is how such heavy?even dependent drinkers? adjust their drinking/driving behavior in order to drive interlock-equipped vehicles and why having made that adjustment they return to their normal drinking-driving behavior once the interlock is removed. This return to preinterlock levels of recidivism is a major limitation on the effectiveness of this rapidly expanding sanction for impaired drivers. To answer that question, this study will collect self-report, biological, and official record data on the drinking and the driving of 500 first DWI offenders sentenced to 6 months on the interlock. Data will be collected covering the 6 months before the interlock is installed, the 6 months when the interlock is on the vehicle, and the 6 months following its removal. The Timeline Followback method will be used to build detailed scenarios of drinking-driving practices in each of those periods. These self-report data will be augmented with objective measures of alcohol consumption from biomarkers in hair and blood and interlock breath tests. Data will be examined to determine the coping methods (e.g., drinking at home versus away from home) used by offenders to avoid lockouts and the trajectories of those coping mechanisms in transition from the pre-arrest period, when the participant was driving under normal legal deterrence conditions, to the period on the interlock when the participant is prevented from driving if drinking, to the 6 months after the interlock is removed. Knowledge about how DWI offenders change their drinking and/or driving behaviors in order to start their cars will be useful to treatment specialists, probation officers, and interlock providers who deal with DWI offenders. More significantly, these results will provide a basis for developing interventions that extend the safety benefits of the altered drinking-driving behaviors adopted while on the interlock into the lifetime of driving following interlock removal.